Passage III

Asteroids and Dinosaurs

[1]

[1] In 1980, physicist Luis Alvarez and his son, geologist Walter Alvarez announced a startling discovery. [2] While analyzing rocks from the same geologic layer in both Europe and New Zealand, traces of iridium were found, an element more common in outer space than on Earth. [3] The iridium came from a single geologic layer dating back 65 million years. [4] Other scientists soon confirmed the discovery: a 65-million-year-old layer of iridium is present around the world. [5] Somewhere, the Alvarezes hypothesized, a large extraterrestrial object must have crashed into our planet, leaving iridium in places thousands of miles apart. (34)

[2]

The search was on for the crater that the object must have left behind. In fact, the crater had been detected by Glen Penfield, on the job as a geologist working in the Yucatan region of Mexico. While measuring underground magnetic fields, Penfield had discovered a circular pattern resembling an impact crater in rocks lying one mile underground. After examining Yucatan rock samples Penfield also discovered telltale "shocked" quartz (37). Microscopic parallel lines in the quartz could only have been created by an incredibly powerful collision. (38)

[3]

These discoveries provided strong evidence that a large asteroid crashed into Earth about 65 million years ago, creating what is known as the Chicxulub crater. Such an impact many scientists believe would have blanketed the planet with debris, blocking out sunlight and cooling Earth for many years. Acid rain created by the debris may have poisoned Earths forests and water.

[4] Many scientists theorize the Chicxulub asteroid event helped bring about the extinction of the dinosaurs, which happened and took place about 65 million years ago. According to this theory, the dinosaurs and about 70 percent of all other species died out because their food and water had been destroyed or poisoned. This mass extinction may also have been the key to the evolution in another life form: mammals.